Generating system regulation



March 19, 1963 w. HALLIDY 3,082,370

GENERATING SYSTEM REGULATION Filed Oct. 50, 1957 2 Sheets-Sheet 1 a /.s' E 2/ INVENTOR. fie"? VV/LL/AM M. HALL/DY BY M W, %w,%

ArrvR/v rs March 19, 1963 w. M. HALLIDY GENERATING SYSTEM REGULATION Filed 001;. 30, 1957 2 Sheets-Sheet 2 INVENTOR.

Mu/AM M //AL 470) Q 9% g I Arrow/0's United States Patent 3,082,370 GENERATING SYSTEM REGULATION William IM. Hallidy, Lakewood, Ohio, assignor'to The Le'ece Neville Compan, Cleveland, Ohio, at corporation of Ohio v Filed Oct. 3il,--1957,Ser. No. 6%,320

2 Claims. (Cl. 32225) This invention relates to volt-ageand current regulaing apparatus and to electrical generating systems embodying such regulating apparatus An objector the inventionis to provide'transistorized regulating apparatus for'controlling voltage and current values and a novel generating system employing such transistorized regulating apparatus.

Another object is to provide a novel regulating apparatus and generating system employing'transistormeans in combination with a low-cost electromagnetic relay means, such that the transistor means provides a desirable long life'for'm of variable impedance and such thatthe contacts of the relay meanshandle only the input signal to the transistor means and will accordingly have a long contact life.

A further object is to provide such a combination transistor-and-relay form of regulating apparatus for application to a current supply means and in which the energizinghcoil means of the relay means is connected with the current supply means through voltage and/or current sensing means.

Still another object is to provide such a combination transistor-and relay'form of regulating apparatus for ap plication to a current supply means and in which the sensing means comprises other transistor means for controlling or amplifying the coil current being supplied to the relay means. i

Yet another object is to provide apparatus of the character above mentioned in which the current supply means comprises generator means whose field excitation is controlled by a transistor means in response to an input signal supplied to the latter through the contacts of the relay means.

1t is also an object of this invention to provide novel sensing means for use with an'alternating current supply means and comprising an amplifying transistor means connected with the current supply means through a. pair of're'c'tifiers and a center-tapped resistor, such that the output signal of the sensing means will always be a lowvoltage direct currentsignal.

Additionally this invention provides novel regulating means for application to an alternating current generating system, inwhi'ch the field excitation of the generator means is controlled by' afirst transistor means in-response to an input signal supplied to the latter through the contacts of a-relay means, and in which the coil current of the relay means issupplied thereto by a sensing means 3,082,370 Patented Mar. 19, 1963 2 current generating systems embodying the voltage and current regulating means of the present invention; and

FIGS. 4, 5 and 6 are wiring diagrams showing alterhating current generating systems embodying the regu lating means of this invention. 7

As representing one of the preferred embodiments of the present invention, FIG. 1 shows regulating means 10 applied to a direct currentgenerating system 11 and comprising in general a power transistor 12, a voltage relay 13, and a load limiter or current relay 14.

The generating. system llincludes a direct current generator 15 having positive and negative output or load terminals1'6 and 17 and a shunt field winding 18. The

comprising an amplifying transistor means 'COHHGC'EGd system 11 also includes an external load circuit comprising load conductors 1'9 and .20 connected to the load terminals .16 and 17 respectively for supplying current to external load devices such as lamps 21 and'a storage battery 22. V

The transistor 12 is a conventional form of transistor having emitter and collector electrodes 24 and 25 and a base electrode 26. The transistor 12 is located in the field circuit of the generator 15 with its emitter and collector electrodes 24 and 25 as output electrodes and connected in series circuit with the field winding 18. The transistor 12 can be either a PNP or an NPN transistor depending upon the polarity of the circuit connections employed but; as here shown, is a PNP transistor having its emitter electrode 24 connected with the positive load terminal '16 of the generator 15 through the load conductor 19. The voltage relay 13 is of a conventional for'm comprising an energizing magnet coil 27 mounted on a suitable frame (not shown), and a-movable armature 28 which is responsive to the energization of the magnet coil. The voltage relay 13 also comprises a pair of stationary and movable contacts '30 and 31, of which the movable contact 31 is carried by the armature 28 and is biased toward engagement with the stationary contact by. a tension spring 32 connected with the armature.

The magnet coil 27 of the voltage relay 13 is connected across the output terminals 16 and 17 of the generator 15 through the load conductors 19 and 20, so as to be responsive to variations in the output voltage of the generator. :For this purpose, oneend of the magnet coil 27 is connected with the load conductor 19 by a 'conductor 33 andthe other end of'this coil is cionnected 'to'the'load conductor 20 through aresistance device or voltage divider'34 which is preferably of the potentiometer type. The resistance device 34"comprises a resistor 35 connected a'crosstheload terminals 19 and 20 and a 'shiftable contact 36' movable alongthe resistor 35 and having such other-end of the magnet coil 27 connected therewith by the conductor 37.

The load limiter or currentrelay '14is of a conventionalfor'm comprising an energizing magnet coil- 40- mounted on a suitable magnet frame (not shown) and a movable armature 41 whichis responsive to the energization of "the magnetcoil40. The current relay 1 4 also comprises cooperating stationary and movable contacts 42 and 43,

of which the lattercontact is carried by the armature 41 andis biased toward engagement with the stationary contact 42 by a tension spring 44 connected to the armature. The energizing coil 40 of the current relay 14 is a series coillocated in the load conductor 19,'s,uch that the energization of this coil will be responsive to changes 3 in the current values of the load current being delivered by the generator 15.

The regulating apparatus also comprises a signal or control circuit means through which a signal or control potential is supplied to the base 26 of the transistor 12 and is controlled by the cooperating contacts of the voltage and current relays 13 and 14. This control circuit means is here shown as comprising a conductor 46 connecting the voltage relay armature 28 with the base 26 of the transistor 12, a conductor 47 connecting the armature -41 of the current relay 14 with the stationary contact 30 of the voltage relay, and a resistor 48 connected between the stationary contact 42 of the current relay and the load conductor 20.

The voltage and current relays 13 and 14 are of the vibratory type and, from the construction and circuit connections above described for the regulating means 10, it will be seen that the voltage relay will be responsive to variations in the output voltage of the generator 15 and the current relay 14 will be responsive to variations in the load current being delivered by the generator. It Will be seen further that the signal current, being supplied to the base 26 of the transistor 12 through the above-mentioned control circuit, passes through the voltage and current relay contacts 30, 31 and 42, 43. Consequently, whenever either pair of these contacts is open in response to an increase occurring in the voltage or current value of the generator output, the control circuit will be opened to interrupt the supply of signal cur rent to the base of the transistor.

The transistor 12 will accordingly serve as a variable impedance in the field circuit of the generator 15 and will also function as a true switching device inasmuch as the circuit to the transistor base 26 is either open or closed depending upon the condition of the contacts of the voltage and current relays 13 and 14. When the voltage and current values of the output of the generator 15 are low, both pairs of regulator contacts will be closed by the influence of the springs 32 and 44 whereupon signal current will be supplied to the transistor base 26 cansing the transistor to conduct. Thereupon a full value of field energizing current will flow through the emitter and collector electrodes 24 and 25 and through the field winding 18 of the field circuit. In response to a resulting build-up of the voltage and current values of the generator output, one or both of the pairs of contacts 30, 31 and 42, 43 of the voltage and current relays 13 and 14 will be opened to thereby interrupt the signal current supply to the transistor base 26, whereupon the transistor will be in a non-conducting or off condition and the energizing current flowing through the field Winding 18 will be of a minimum or zero value.

The resistor 48 of the above-mentioned control circuit is selected of a suitable resistance value such that when the transistor 12 is in an on or conducting condition, the current flow through the emitter and collector electrodes thereof will be limited to a safe value for the transistor but will still provide full excitation for the field winding 18.

The regulating means 10 preferably also includes a suitable diode 50 connected in a shunt relation to the field Winding 18 for protect-ing the transistor 12 by dissipating the induced potential or so-called inductive kick of the field winding.

FIG. 2 of the drawings shows transistorized regulating means 52, similar to the regulating means 10 above described and applied to a direct current generating system 53 which is similar to the above-described generating system 11. The components of the regulating means 52 and of the generating system 53, which correspond with components of the regulating means 10 and of the generating system 11, have been designated by the same reference characters.

The voltage relay 13a of the modified regulating means 52 differs from the above-described voltage relay 13 in that it is a double-contact type of voltage relay having a second pair of cooperating contacts 54 and 55, of which the contact 54 is a stationary contact spaced from the stationary contact 30 and the contact 55 is a movable contact carried by the armature 28. The stationary contact 54 is connected with the load conductor 19 by a conductor 56. The resistance value of the resistor 56 can be varied to suit the circuit requirements of the regulating means 52 and, if desired, can be omitted.

The second pair of contacts 54 and 55 of the voltage relay 13a, when closed, serves to apply a signal bias to the transistor base 26 or to substantially short-circuit the emitter and base electrodes, such that the transistor 12 will be completely out oflf. Thus, whenever the output voltage of the generator 15 rises above a predetermined value to cause such closing of the second pair of contacts 54 and 55, the transistor 12 will be in a completely off condition causing a sudden and complete collapse of the field fiux. Although opening of the voltage relay contacts 30 and 31 will convert the transistor 12 to an off condition by opening the signal circuit to the transistor base 26, a fiow of leakage current may still take place through the emitter and collector electrodes of the transistor, whereas the closing of the second pair of contacts 54 and 55 will insure the transistor being converted to the off condition to effectively deenergize the field winding 18 and quickly correct any abnormal voltage condition of the load circuit. The portion of the field circuit which connects the emitter 24 of the transistor 12 with the load conductor 19 is here shown as having a resistor 57 of suitable value therein although, if desired, this resistor can be omitted.

FIG. 3 of the drawings shows another form of transistorized regulating means 60 applied to a direct current generating system 61 which is substantially the same as the above-described generating systems 11 and 53. The regulating means 60 employs the same power transistor 12 and voltage relay 13a as are used in the regulating means 52 of FIG. 2. The other components of the regulating means 60 and of the generating system 61 which correspond with those above described, are designated by the same reference characters.

The regulating means of FIG. 3 differs from the abovedescribed regulating means 10 and 52 of FIGS. 1 and 2, in that the stationary contact 30 of the voltage regulator 13a is connected directly with the load conductor 20 through a resistor 48a, and in that the magnet coil 27 of the voltage relay 13a is connected with the output terminals of the generator 15 through transistorized voltage and current sensing devices 62 and 63.

The voltage sensing devices 62 comprise a transistor 65, a diode 66, and a resistance device 67 which is preferably of the potentiometer type. The transistor 65 is used as a signal amplifying transistor and is of a conventional form having emitter, collector and base electrodes 68, 69 and 70. The emitter electrode 68 is connected with the load conductor 19 by the conductor 71 and the collector electrode 69 is connected with one end of the voltage relay magnet coil 27 through the conductor 72. The other end of the magnet coil 27 is connected with the load conductor 20 by a conductor 7 3.

The resistance device 67 comprises a resistor 75 connected across the load conductor 19 and 20, and a shiftable contact 76 movable along the resistor 75 and connected with the base 70 of the transistor 65 through the diode 66.

The diode 66 is of the Well known Zener type and is one having a relatively low breakdown voltage such that the voltage sensing device 62 will be responsive to relatively low-value voltage fluctuations in the load output of the generator 15. Thus when voltage increases above a predetermined value occur in the generator output, the diode 66 will become conductive and will apply voltage signals to the base 70 of the transistor 65, resulting in this transistor becoming conductive and supplying an amplified control current to the magnet coil 27 of the voltage relay 13a for the functioning of the latter in the manner already explained above in connection with the regulating means and 52 of FIGS. 1 and 2.

The current sensing device 63 comprises a series resistor 78in the load conductor 19, a transistor 79, and a diode 80. The transistor 79 is-of a conventional'form comprising emitter and collector electrodes 81 and 82 and a base electrode 83-. The emitter electrode 81 is connected with the load conductor 19 on one side, in this case the generator side, of the series resistor 78 by a conductor 84, and the collector electrode 82 is connected with one end of the voltage regulator coil 27 througha portion of the. conduc'tor 72 and a circuit connection 85.

The diode 80 can be of a conventional form and preferably has a low breakdown voltage so as to render the current sensing device 63 responsive to current fluctuations in the output of the generator which exceed a predetermined permissible'load current by only relatively small values. The diode 80 is connected to the base 83 of the transistor 79 by a conductor 87 and to the load conductor 19 at a point on the other or load side of'a series resistor 78 by a conductor 86.

Thus the diode 80 is connected in a shunt relation to the series resistor 78 and, when the IR drop acrossthe series resistor exceeds the breakdown voltage of this diode, a

current signal will be applied to the base 83 and the trait-- sistor 79 will then conduct. The transistor 79 functions as an amplifying transistor and responds to the current signal applied to the base 83 thereof by supplying a relatively larger coil-energizing current to the voltage relay coil 27.

From the circuit connections and functioning of the voltage and current sensing devices 62 and 63 as above described, it will be seen that the transistors-65 and 79 will function as switching transistors as well as amplifying transistors. Thus, when the voltage and current values of the generator output are relatively low, these transistors will be in an oif condition and the voltage relay coil 27 will be substantially deenergized, but when either of the voltage and current values of the generator outputexceeds a predetermined value, the transistor of the corresponding sensing devices will become conductive and will supply amplified energizing current to the voltage relay coil 27.

In the regulating apparatus 60, the transistors 12, 65 and .79 can be conveniently referred to as the first, second and third transistors respectively. The transistors 65 and 79 can be PNP- or NPN transistors, depending upon the polarity of the circuit connections employed, and as here used are of the. PNP type.

FIG. 4 of the drawings shows transistorized regulating means'90 applied to an alternating cu'rrent'generating system 91 which includes an exciter' generator 92. The regulating means 90-coznprises thesame components as the regulating means 52 of FIGJ2, namely a power transistor 12, a voltage regulator 13a'and 'a load limiter or current relay- 14, but they are differently located, as will be explained presently.

The alternating current generating system 91 includes an alternator-93 having a field winding-94 to which the positive and negativeoutput terminals 95 and 96 of the excite'r generator 92 are connected by conductors '9 7 and 98. The alternator 93 has output terminals 99 and 100 to which a'pair of load conductors 102 and 103 are connected respectively for supplying current to an external load such as to lamps 104. The exciter generator 92 includes a conventionalshunt field winding 105 on which the regulating means 90 is effective in substantially the same manner as'has been described above in connection with the control action of the regulating means 10-and 52 on the field winding 18 of the direct current generator 15.

In the application of the regulating means 90 to the alternating current generating system 91, the magnet coil 27 of the voltage relay 1311 has one end thereof connected with the load conductor 102 by a conductor 107 and its other end connected to the alternator'93 through a potentiometer-type of resistance device 108 and aconductor 109. The resistance device 108 comprises a resistor 110 connected across the load conductor 102 and 103, and a movable contact 111 shiftable along the'resistor 110 and having such other end of the voltage relay coil 27 connected therewith by the conductor 109. The series mag net coil 40 of the current relay 14 is located in the load conductor 102r of this alternating current generating sys-- tem.

From the construction and the circuit connections just above described for the regulatingmeans 90 and the alternating current generating system 91 of FIG. 4, it will be seen that the regulating means will be directly responsive to voltage and current fluctuations in the alternating current output of the system 91 such that the transistor 12 will control the excitation of'the field winding 105 of the e);- citer 9 2, with the result that the output ofthe exciter' will correspondingly vary the excitation of the field winding 94 of the alternator 93 and produce a controlled effect on the voltage and current values of the alternator output being'supplied to the load circuit.

The regulating means 90 preferably includes a diode 106 in shunt relation to the'ex'citer field'105'for protecting the transistor 12 against the inductive effects of the field winding in the manner already explained above for the diode 50 of FIG. 1.

FIG. 5 of the drawings shows transistorized regulating means 115 which, in certain respects, issimilar to the above-described regulating means 90 and which is applied to an alternating current generating system of substantiah ly the same form as the above-described alternating current generating system 91 of FIG. 4. The components of the regulating means 115 and of the generating system 116, which correspond with those of the regulating means and generating system 91, have been designated by the same reference characters. The regulatingmeans of FIG. 5 ditfersfrom the regulating means 90- in that the load limiter or current relay 14 has been omitted, and in the use of a dilferent form of voltage sensing device 117.

The voltage sensing device 117 includes a first centertapped resistor 118 connected across the load conductors 102 and 103 and having a center tap .119 to which one end of the voltage relay magnetcoil 27-isconnected by acon= ductor 120'. The voltage sensing device 117 also includes a second center tapped resistor 121 connected across the load conductors 102 and 103- and having .a center tap'1'22. Additionally the voltage sensing device 117 comprises a transistor 123, a pair of diodes used as rectifiers 124 and 125, and a diode 126 of the Zener type and having a low breakdown voltage.

The transistor 123 is of a conventional form having emitter and collector electrodes 127 and 128 and a base electrode 129. The transistor 123 functions as both-a switching transistor and an amplifying transistor. The base 129 of the transistor is connected withthe center'tap 122 of the resistance device- 121 through the diode 126. The center tapped resistor 121 forms a part of a variable resistance device 131 whicl1 also includes adjustable contacts 132 and 133 shiftable along end portions or resistance sections 1210: and 121b of the resistor 121.

The diodes 124 and are half-Wave rectifiers which are connected respectively with thecontacts 132 and 133 by'conductors 134-and 135 and are also connected with each other by a junction conductor 136. The emitter electrode 127 of the transistor 123 is connected with the rectifiers 124 and 125 at a point therebetween by a conductor 137. The collector electrode 128 of the transistor 123 is connected with the other end of the voltage relay coil 7 i 27 through a conductor 138.

From the'construction and circuit connections of the voltage sensingdevice 117 as above described, it will be seen that the voltage relay 13a will be responsive to-relatively low-value voltage fluctuations occurring in the output of the alternator 93 and that the voltage sensing means itself will be subjected to only relatively low voltage values by reason of the use of the center-tapped resistors 118 and 121 for connecting this sensing means in circuit with the alternator. It will also be seen that, by reason of the use of the pair of rectifiers 124 and 125, the alternating current signals supplied to the sensing device 117 by the load conductors 102 and 103 Will be rectified with respect to both half-Wave portions of the alternating current output, such that the energizing current supplied to the voltage relay coil 27 by the sensing means will be a full-Wave rectified DC. current. V

Moreover, it will be seen that by use of the adjustable contacts 132 and 133 of the resistance device 131 as the circuit connections to the pair of rectifiers 124 and 125, the voltage of the rectified current being supplied to the voltage relay coil 27 can be maintained at a suitably low value which will be a safe value for the transistor 123 and will permit the latter to be of a small and inexpensive size. Additionally it will be seen that by using as the diode 126 a conventional diode having a low breakdownvoltage, the transistor 123 Will be responsive to low voltage fluctuations in the output of the alternator 93 and will be switched to an on or conducting condition in response to signals of a relatively low voltage value. It will be seen further that the voltage relay coil 27 will be energized only when the transistor 123 is in its on condition and that when this transistor is switched to its off condition, the voltage relay coil will be substantially deenergized.

The transistors 12 and 123 of the regulating means 115 can be conveniently referred to as the first and second transistors.

FIG. 6 of the drawings shows transistorized regulating means 140 which is generally similar to the regulating means 115 of FIG. and is applied to an alternating current generating system 141 which is substantially the same as the above-described alternating current generating system 116 of FIG. 5. The regulating means 148 differs from the above-described regulating means 115 in that it employs a novel current sensing device 142 in addition to the voltage sensing device 117.

The current sensing device 142 comprises a series resistor 143 located in the load conductor 102 and a third transistor 144 which is used as both a switching transistor and an amplifying transistor. The current sensing device 142 also comprises a diode 145 of a low breakdown voltage and a pair of diodes operating as half-wave rectifiers 146 and 147.

The transistor 144 is of a conventional form having emitter and collector electrodes 148 and 149 and a base electrode 150. The series resistor 143 is a center tapped resistor having a center tap 152 to which the base 150 of the transistor 144 is connected through the diode 145. The rectifiers 146 and 147 are connected with the load conductor 102 on opposite sides of the series resistor 143 by conductors 153 and 154. The emitter electrode 148 of the transistor 144 is connected with the rectifiers 146 and 147 at a point therebetween by being connected to a junction conductor 155 extending between the rectifiers. The collector electrode 149 of the transistor 144 is connected with the same end of the voltage relay coil 27 as the voltage sensing means 117, through a portion of the common conductor 138 and through a circuit connection 156.

From the construction and circuit connection above described for the current sensing device 142, it will be seen that this device will supplement and cooperate with the voltage sensing device 117 for energizing the voltage relay coil 27 in accordance with current and voltage variations in the output of the alternator 93. It will also be seen that the current sensing device 142 will be responsive to current variations of a relatively low value occurring in the load circuit inasmuch as the diode 145 has a relatively low breakdown voltage and will become conductive to apply a current signal to the base 159 of the transistor 144 whenever the current variation in the load circuit 61166668 a predetermin d value represented by a 8 predetermined increase in the IR drop across the series resistor 143.

Thus whenever the diode becomes conductive and supplies a current signal to the base 150, the transistor 144 Will be switched to a conducting or on condition during which it will cause current to be supplied to the voltage relay coil 27 and, by reason of the use of the pair of half- Wave rectifiers 146 and 147, the energizing current thus supplied to the voltage relay coil will be a continuous rectified DC. current resulting from the rectification of both half-waves of the alternating current of the load circuit. By reason of the switching action of the transistor 144, the current supplied to the voltage relay coil will be of a maximum value when a current signal is supplied to the base through the diode 145 and will be of a zero value when the transistor is in its oil condition. By reason of the amplifying use of the transistor 144, the current thus supplied to the voltage relay coil 27 while the transistor is in its on condition will be an amplified current.

From the accompanying drawings and the foregoing detailed description it will now be readily understood that this invention provides a novel and highly effective form of regulating means for application to a current supply means and which utilizes the desirable long-life characteristics of a transistor means and the desirable low-cost characteristic of voltage and current relays of the electromagnetic type. It will also be understood that the invention provides novel electrical generating systems employing such a combination transistor-and-relay type of regulating means. Additionally it will be seen that this invention achieves the important advantage from such a combination type of regulating means that the power transistor controlling the variable energization of a magnet coil of the current supply means will have a long life and will need to be of a load rating handling only the energizing current of such coil rather than the load current of the load circuit, and also the advantage that this transistor will function as a true switching transistor having an on or off condition depending upon whether control or signal current is being supplied to the base thereof by the voltage and current relays. It will be seen furthermore that another important advantage is realized in that the contacts of the low-cost voltage and current relays will need to handle only the signal current being supplied to the base of the power transistor, with the result that the relay contacts will not be subjected to any destructive amount of sparking and will consequently have a long life and will remain in an efiicient operating condition.

Although the novel regulating means of this invention and the novel generating systems embodying the same have been illustrated and described herein to a somewhat detailed extent, it will be understood that the invention is not to be regarded as being limited correspondingly in scope but includes all changes and modifications coming within the terms of the claims hereof.

Having described my invention, I claim:

1. An electric generating system comprising, a generator having load terminals and a field winding, a field circuit for said field winding, a load circuit connected with said load terminals, a relay comprising a magnet coil and vibratory contact means responsive to the energization of said magnet coil, energizing circuit means for said magnet coil, a first transistor having main electrodes in said field circuit and a first control electrode connected to be energized through said vibratory contact means, a second transistor having main electrodes in said energizing circuit means and a second control electrode, a third transistor having main electrodes in said energizing circuit means and a control electrode, and means connected to the control electrodes of said second and third transistors to control energization thereof in depedence upon voltage across and current in said load circuit.

2. An electric generating system comprising, a generator having load terminals and a field winding, a field circuit for said field winding, a load circuit connected with said lead terminals, a relay comprising a magnet 9 coil and contacts responsive to energization of the relay coil, a first transistor having main electrodes in said field circuit and a control electrode connected to be energized under the control of said contacts, second and third transistors each having main electrodes and a control electrode, the main electrodes of each of said second and third transistors being connected to said relay coil to control energization of said relay coil, a pair of voltage responsive breakdown devices connected to the control electrodes of said second and third transistors, and means connected to apply voltages to said breakdown devices dependent respectively upon current in and voltage across said load circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,936,692 2,809,301 Short Oct. 8, 1957 FOREIGN PATENTS 278,060 Great Britain Sept. 22, 1927 Stoller Nov. 28, 1933 

1. AN ELECTRIC GENERATING SYSTEM COMPRISING, A GENERATOR HAVING LOAD TERMINALS AND A FIELD WINDING, A FIELD CIRCUIT FOR SAID FIELD WINDING, A LOAD CIRCUIT CONNECTED WITH SAID LOAD TERMINALS, A RELAY COMPRISING A MAGNET COIL AND VIBRATORY CONTACT MEANS RESPONSIVE TO THE ENERGIZATION OF SAID MAGNET COIL, ENERGIZING CIRCUIT MEANS FOR SAID MAGNET COIL, A FIRST TRANSISTOR HAVING MAIN ELECTRODES IN SAID FIELD CIRCUIT AND A FIRST CONTROL ELECTRODE CONNECTED TO BE ENERGIZED THROUGH SAID VIBRATORY CONTACT MEANS, A SECOND TRANSISTOR HAVING MAIN ELECTRODES IN SAID ENERGIZING CIRCUIT MEANS AND A SECOND CONTROL ELECTRODE, A THIRD TRANSISTOR HAVING MAIN ELECTRODES IN SAID ENERGIZING CIRCUIT MEANS AND A CONTROL ELECTRODE, AND MEANS CONNECTED TO THE CONTROL ELECTRODES OF SAID SECOND AND THIRD TRANSISTORS TO CONTROL ENERGIZATION THEREOF IN DEPEDENCE UPON VOLTAGE ACROSS AND CURRENT IN SAID LOAD CIRCUIT. 